This research deals with the isolation and characterization of new trichothecene antibiotics with emphasis on those compounds which exhibit in vivo anticancer activity. These compounds are isolated from both fermentation of Myrothecium spp. as well as from a large scale extract of the Brazilian shrub, Baccharis megapotamica. In addition to these new natural products, known macrocyclic trichothecenes (e.g., roridins and verrucarins) are to be chemically modified to compounds possessing substantially increased in vivo anticancer activity.